The invention relates to apparatus and methods for aeration of wastewater, and more particularly to improvements that increase the zone of influence, and greatly increase the amount of oxygen transferred to the wastewater per horsepower of energy required.
Wastewater from both municipal sewage systems and from industrial waste product exhausting systems is usually collected in large ponds that are referred to as wastewater lagoons. Such lagoons may be 5 to 15 feet deep and may cover quite a number of acres of surface area. The wastewater usually includes large amounts of organic and inorganic waste material that, if left untreated, creates severe odors and generates toxic products. Seapage of toxic products in wastewater lagoons into ground water reservoirs and the resulting contamination is a serious problem that only recently is receiving grudging attention from many municipal governments.
Any wastewater lagoon has a basic requirement for an amount of oxygen that must be dissolved to prevent the lagoon from "turning sour", or becoming anaerobic. With its basic oxygen demand (BOD) being met by dissolving a minimum amount of oxygen into the wastewater, the sewage will undergo biodegradation that converts the wastewater into a relatively nontoxic, nonoffensive effluent. If the basic oxygen demand is not met, sludge deposits build up on the bottom, causing odors and toxic conditions that become progressively worse, increasing the spread of the resulting contamination both through the air and ground water seepage. Municipal governments often have ignored the problem as much as possible, due to the very high cost of prior techniques of introducing enough oxygen into the wastewater lagoons to meet the BOD requirements. Various approaches have been used, typically by surface aeration or by submerged aeration systems wherein air is pumped below the surface of the water, sometimes below a rotating impeller that shears the rising air into smaller bubbles and mixes the wastewater and entrained air. Both radial flow and axial flow impellers have been used, as indicated in U.S. Pat. No. 3,846,516. The state-of-the-art also is indicated in U.S. Pat. Nos. 4,543,185 and 3,521,864.
Various mixing devices are known for mixing finely ground ore with leaching ores. One such mixing device that has been in use for about 50 years uses an impeller similar to the impeller of the wastewater aeration apparatus of my invention. The impeller of the ore mixing device causes air to be incidentally mixed with the finely ground ore and leaching fluids.
All of the installed prior systems of which I am aware for aeration of wastewater have consumed tremendously large amounts of electrical power to run the pumps associated therewith, and have performed below initial expectations of the users. In a number of instances of which I am aware, wastewater aeration systems costing millions of dollars have been installed, and when operated have consumed tremendously large amounts of electricity, yet have failed to raise the dissolved oxygen level in the wastewater lagoons to an acceptable level, and in some cases have been shut down in a short time due to their ineffectiveness and/or cost.
It is clear that there is a great long-existing, unmet need for an apparatus and method for aerating wastewater lagoons that are much less expensive to install and operate than prior wastewater aeration systems, and which are much more efficient with respect to amount of oxygen dissolved per unit volume of wastewater per unit of required operating energy.